FT-IR, FT-Raman, SERS spectra and computational calculations of 4-ethyl-N-(2'-hydroxy-5'-nitrophenyl) benzamide

Article abstract of DOI:10.1002/jrs.2471

Fourier transform infrared (FT-IR) and FT-Raman spectra of 4-ethyl-N-(2'hydroxy-5'-nitrophenyl) benzamide were recorded and analyzed. A surface-enhanced Raman scattering (SERS) spectrum was recorded in silver colloid. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red shift of the NH stretching wavenumber in the infrared spectrum from the computational wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. The simultaneous IR and Raman activation of the C O stretching mode gives the charge transfer interaction through a π-conjugated path. The presence of methyl modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface, which affects the orientation and metal molecule interaction. The first hyperpolarizability and predicted infrared intensities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive subject for future studies of nonlinear optics. Optimized geometrical parameters of the title compound are in agreement with reported structures.

Full text of DOI:10.1002/jrs.2471

Research Article
Received: 12 April 2009
Accepted: 29 July 2009
Published online in Wiley Interscience: 23 September 2009
(www.interscience.wiley.com) DOI 10.1002/jrs.2471
FT-IR, FT-Raman, SERS spectra and
computational calculations of 4-ethyl-N-(2ꢀ-
hydroxy-5ꢀ-nitrophenyl)benzamide
C. Yohannan Panicker,a∗ Hema Tresa Varghese,b L. Ushakumari,a
Tugba Ertan,c Ilkay Yildiz,c Carlos M. Granadeiro,d Helena I. S. Nogueirad
and Y. Shyma Marye
Fourier transform infrared (FT-IR) and FT-Raman spectra of 4-ethyl-N-(2ꢀ-hydroxy-5ꢀ-nitrophenyl)benzamide were recorded and
analyzed. A surface-enhanced Raman scattering (SERS) spectrum was recorded in silver colloid. The vibrational wavenumbers
and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes.
The red shift of the NH stretching wavenumber in the infrared spectrum from the computational wavenumber indicates the
weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. The simultaneous IR and Raman
activation of the C O stretching mode gives the charge transfer interaction through a π-conjugated path. The presence
of methyl modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface, which affects the
orientation and metal molecule interaction. The first hyperpolarizability and predicted infrared intensities are reported. The
calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive subject for
future studies of nonlinear optics. Optimized geometrical parameters of the title compound are in agreement with reported
c
structures. Copyright ꢀ 2009 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: benzamide; FT-IR spectra; FT-Raman spectra; DFT calculations; SERS; hyperpolarizability
Introduction
as a class of compounds with a wide variety of interesting bi-
ological activities, including antimycobacterial and antifungal
effects.[17–21] Arslan et al.[22] reported the molecular structure
and vibrational spectra of 2-chloro-N-(diethyl carbamothioyl) ben-
zamide by Hartree–Fock (HF) and density functional methods.
Takeuchi et al.[23] reported the molecular structure of benzamide
as studied by gas-phase electron diffraction. Gas-phase structures
of fundamental amides, formamide,[24] and acetamide[25] were
determined by electron diffraction, and their crystal structures
were studied by X-ray and neutron diffraction.[26–30] The crystal
structures of benzamide were determined by X-ray and neu-
trondiffraction.[31,32] Thehydrogen-bondinginteractionsbetween
In the past few decades, the dramatically rising preva-
lence of multidrug-resistant microbial infections has be-
come a serious healthcare problem. In particular, the emer-
gence of multi-drug resistant strains of Gram-positive bac-
terial pathogens such as methicillin-resistant Staphylococcus
aureus and Staphylococcus epidermis and vancomycin-resistant
Enterococcus is a problem of ever-increasing significance.[1–5]
Benzamide derivatives exhibit various types of biologi-
cal properties such as anthelmentic, antihistaminic, antifun-
gal, and antibacterial.[6–14] 6-N-(2-Hydroxy-3,5-dichlorophenyl)-
2-hydroxy-3,5,6-trichlorobenzamide (oxyclozanide), which has a
benzamide structure, was discovered in 1969 as an anthelmentic
agent effective against Fasciola hepatica for the treatment of liver
fluke infection.[6] 3,4-Dihydroxy-6-(N-ethylamino)benzamide is a
natural product that has been found in green pepper (Pipernigrum
L.)asanantibacterialbyPradhanet al.[11] Additionally,abenzamide
derivative, BAS-118, has been found to be a novel anti-Helicobacter
pylori agent with a potent and selective antibacterial activity,
which includes clarithromycin (CAM)- and metronidazole (MNDZ)-
resistant isolates.[15] Yalcin et al.[10,12–14] reported some novel
microbiologically active N-(2–hydroxy-5-substitutedphenyl) ben-
zamide/phenyl acetamide/phenoxy acetamide/thiophenoxy ac-
etamide derivatives. The synthesis and biological evaluation of
N-(2-hydroxy-4(or5)-nitro/aminophenyl) benzamides and phenyl
acetamides as antimicrobial agents have been reported by Er-
tan et al.[16] 2-Hydroxy-N-phenylbenzamides have been reported
∗
Correspondenceto:C. Yohannan Panicker,DepartmentofPhysics,TKMCollege
of Arts and Science, Kollam 691 005, Kerala, India.
E-mail: cyphyp@rediffmail.com
a
b
c
DepartmentofPhysics,TKMCollegeofArtsandScience,Kollam691005,Kerala,
India
Department of Physics, Fatima Mata National College, Kollam 691 001, Kerala,
India
Faculty of Pharmacy, Department of Pharmaceutical Chemistry, Ankara
University, Tandogan 06100, Ankara, Turkey
d
e
Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro,
Portugal
Thushara, Neethinagar-64, Pattathanam, Kollam 691 021, Kerala, India
c
J. Raman Spectrosc. 2010, 41, 381–390
Copyright ꢀ 2009 John Wiley & Sons, Ltd.

C. Y. Panicker et al.
thioacetamide and several N,N-disubstituted benzamides have
been studied using near-infrared absorption spectroscopy.[33]
Kawski et al.[34] reported the X-ray and IR investigation as well
as quantum mechanical calculations of 2-hydroxy-benzamides.
To our knowledge, no theoretical HF or density functional the-
ory (DFT) calculations, or detailed vibrational infrared and Raman
analyses, have been performed on the title compound. A detailed
quantum chemical study will aid in understanding the vibrational
modes of the title compound and clarifying the experimental data
available for this molecule. DFT calculations are known to provide
excellent vibrational wavenumbers of organic compounds if the
calculatedwavenumbersarescaledtocompensatefortheapprox-
imate treatment of electron correlation, for basis set deficiencies,
and for the anharmonicity effects.[35–40] DFT is now accepted as
a popular post-HF approach for the computation of molecular
structure, vibrational wavenumbers, and energies of molecules by
the ab initio community.[41] In this work, by using HF, B3PW91
and B3LYP methods, we calculated the vibrational wavenumbers
of the title compound in the ground state to distinguish the fun-
damentals from the many experimental vibrational wavenumbers
and geometric parameters. These calculations are valuable for
providing insight into the vibrational spectrum and molecular pa-
rameters.Thesurface-enhancedRamanscattering(SERS)spectrum
is also recorded and analyzed.
Figure 1. FT-IR spectrum of 4-ethyl-N-(2ꢁ-hydroxy-5ꢁ-nitrophenyl)
benzamide.
Experimental
Thechemicalswerepurchasedfromcommercialvendorsandused
without purification. The reactions were monitored and the purity
of the product was checked by thin-layer chromatography (TLC).
Silica gel 60 F254 chromatoplates were used for TLC. The solvent
systems were chloroform/methanol (15 : 1). The final compound
was purified by recrystallization in ethanol. The melting point was
measured with a capillary melting point apparatus (Buchi SMP
20 and Electrothermal 9100) and is uncorrected. The yield was
calculated after recrystallization. The Fourier transform infrared
(FT-IR) spectrum (Fig. 1) was recorded on a Jasco FT/IR-420
spectrometer with KBr pellets. The FT-Raman spectra (Figs. 2 and
3) were obtained on a Bruker RFS 100/S, Germany. For excitation
of the spectrum, the emission from a Nd : YAG laser was used
(excitation wavelength 1064 nm, maximum power 150 mW). The
measurements were made on solid sample. The aqueous silver
colloid used in the SERS experiments was prepared by reduction
ofsilvernitratebysodiumcitrate,usingtheLee–Meisermethod.[42]
Solutions of the title compound were made up in ethanol
(0.1 mmol in 1 ml of solvent) and transferred by a microsyringe
into the silver colloid (10 µl in 1 ml of colloid) such that the
overall concentration was 10−3 mol dm−3. Colloid aggregation
was induced by addition of an aqueous solution of MgCl2 (1 drop
of a 2 mol dm−3 solution). Polyvinylpyrrolidone was then used to
stabilize the colloid (1 drop of 0.1 g 10 ml−1 aqueous solution).
The final colloid mixture was placed in a glass tube and the Raman
spectrum registered.
Figure 2. FT-Raman spectrum of 4-ethyl-N-(2ꢁ-hydroxy-5ꢁ-nitrophenyl)
benzamide.
Figure 3. SERS spectrum of 4-ethyl-N-(2ꢁ-hydroxy-5ꢁ-nitrophenyl)
benzamide.
The 1H NMR spectra was recorded by employing a VARIAN
Mercury 400 MHz FT spectrometer; the chemical shifts (δ) are in
parts per million relative to TMS, and coupling constants (J) are
reported in Hertz. Elemental analyses were carried out on a Leco
932 CHNS-O analyzer. The results of the elemental analyses (C, H,
N) were within 0.4% of the calculated amounts.
in turn by treating p-ethylbenzoic acid with thionyl chloride.
Thionyl chloride (1.5 ml) and p-ethylbenzoic acid (0.5 mmol) were
refluxed in benzene (5 ml) at 80 ◦C for 3 h, and then excess thionyl
chloride was removed in vacuo. The residue was dissolved in ether
(10 ml), and the solution was added during 1 h to a stirred, ice cold
mixtureof2-amino-4-nitrophenol(0.5 mmol), sodiumbicarbonate
(0.5 mmol), diethyl ether (10 ml), and water (10 ml). The mixture
The synthesis was performed by reacting 2-amino-4-
nitrophenolwithp-ethylbenzoicacidchloride,whichwasobtained
c
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Copyright ꢀ 2009 John Wiley & Sons, Ltd.
J. Raman Spectrosc. 2010, 41, 381–390

Vibrational spectroscopy of 4-ethyl-N-(2ꢁ-hydroxy-5ꢁ-nitrophenyl)benzamide
Figure 4. Optimized geometry of 4-ethyl-N-(2ꢁ-hydroxy-5ꢁ-nitrophenyl)benzamide.
wasstirredovernightatroomtemperatureandfiltered.Theprecip-
itatewaswashedwithwater, 2NHCl, water, respectivelyandfinally
with ether to give the compound. The crude product was purified
by recrystallization from ethanol. The crystal was dried in vacuo.
M.p. 254–256 ◦C; Yield 46%; Elemental analyses: calculated:
C62.93, H 4.93; N 9.79; found: C 62.58; H 5.218; N 9.788. 1H NMR
(DMSO-d6) δ ppm J (in Hz): 1.21 (t, 3H, CH3), 2.69(q, 2H, CH2),
7.08(d, 1H, J0 = 9.2, 3ꢁ-H); 7.38(d, 2H, J0 = 8.4, 3-H, 5-H); 7.91(d,
2H, J0 = 8.8, 2-H, 6-H); 7.99(dd, 1H, J0 = 9.2 and Jm = 2.8, 4ꢁ-H);
8.78(d, 1H, Jm = 3.2, 6ꢁ-H); 9.55(s, 1H, OH).
for obtaining a considerably better agreement with experimental
data.[45] Scaling factors 0.9613 and 0.8929 have been uniformly
applied for the DFT- and HF-calculated wavenumbers.[44] The ob-
served disagreement between theory and experiment could be a
consequence of the anharmonicity and of the general tendency
of the quantum chemical methods to overestimate the force con-
stants at the exact equilibrium geometry.[40] The assignments of
the calculated wavenumbers is aided by the animation option of
the MOLEKEL program, which gives a visual presentation of the
vibrational modes.[46,47]
Computational Details
Results and Discussion
The vibrational wavenumbers were calculated using the Gaus-
sian03 software package on a personal computer.[43] The com-
putations were performed at HF/6-31G∗, B3PW91/6-31G∗, and
B3LYP/6-31G∗ levels of theory to get the optimized geome-
try (Fig. 4) and vibrational wavenumbers of the normal modes
of the title compound. Parameters corresponding to optimized
geometry of the title compound are given in table S1 (Sup-
porting Information). The DFT partitions, the electronic energy
E = ET +EV +EJ +EXC, where ET, EV, and EJ are electronic kinetic en-
ergy, electron nuclear attraction, and electron–electron repulsion
terms, respectively. The electron correlation is taken into account
in the DFT via the exchange-correlation term EXC, which includes
exchange energy arising from the antisymmetry of the quantum
mechanical wave function and dynamic correlation in the motion
of individual electron, and it makes the DFT calculations domi-
nant over conventional HF procedure.[44] DFT calculations were
carried out with Becke’s three-parameter hybrid model using the
Lee–Yang–Parr correlation functional (B3LYP) method. Molecular
geometries were fully optimized by Berny’s optimization algo-
rithm using redundant internal coordinates. Harmonic vibrational
wavenumbers were calculated using analytic second derivatives
to confirm the convergence to minima in the potential surface.
At the optimized structure of the examined species, no imaginary
wavenumber modes were obtained, proving that a true minimum
on the potential surface was found. The optimum geometry was
determinedbyminimizing theenergywithrespecttoallgeometri-
cal parameters without imposing molecular symmetry constraints.
The DFT hybrid B3LYP functional tends also to overestimate the
fundamental modes; therefore, scaling factors have to be used
The observed IR and Raman bands with their relative intensities
and calculated (scaled) wavenumbers and assignments are given
in Table 1.
IR and Raman spectra
The OH group provides three normal vibrations: the stretching
vibration υOH, and the in-plane and out-of-plane deformations
δOH and γ OH. The B3LYP calculations give the υOH band at
3604 cm−1. The in-plane OH deformation[48] is expected in the
region 1400 40 cm−1, and the band at 1410 cm−1 in the Raman
spectrum and 1405 cm−1 by DFT is assigned as this mode, which
is not pure but contains significant contribution from phenyl
ring-stretching modes. The stretching of the hydroxyl group with
respect to the phenyl moiety υ(C–O)h appears at 1272 cm−1 in
the Raman spectrum, and the calculated value is 1268 cm−1. This
band is expected in the[49–51] region 1220 40 cm−1. The out-
of-plane OH deformation is expected[48] generally in the region
650 80 cm−1, and in our case it is at 632 cm−1 in the IR spectrum
and at 628 cm−1 theoretically. For paracetamol, υ(C–O)h and γ OH
are reported at 1240 and 620 cm−1, respectively.[52]
The vibrations of the CH2 group (the asymmetric stretch υasCH2,
symmetric stretch υsCH2, the scissoring vibrations δCH2, and
the wagging vibration ωCH2) appear in the regions 2940 20,
2885 45, 1440 10, and 1340 25 cm−1, respectively.[48,50]
These bands are observed at 2971, 1431 cm−1 in the IR spectrum,
2976, 2920, 1457 cm−1 in the Raman spectrum, and at 2963, 2929,
1459, 1319 cm−1 theoretically for the title compound. According
to literature,[53] the scissoring mode of the CH2 group gives rise to
c
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Copyright ꢀ 2009 John Wiley & Sons, Ltd.
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C. Y. Panicker et al.
Table 1. Calculated vibrational wavenumbers (scaled) as well as measured infrared and Raman band positions and assignments for 4-ethyl-N-(2ꢁ-
hydroxy-5ꢁ-nitrophenyl)benzamide
HF/6-31G∗
B3PW91/6-31G∗
B3LYP/6-31G∗
IR intensity υ(IR) (cm−1
υ (cm−1 IR intensity υ (cm−1
)
)
IR intensity υ (cm−1
)
)
υ(Raman) (cm−1
)
υ(Raman) (cm−1
)
Assignments
3671
3477
3071
3066
3043
3016
3006
3000
2996
2927
2920
2897
2870
2861
131.17
40.94
1.50
3640
3491
3137
3122
3107
3082
3071
3068
3064
3021
3018
2980
2941
2940
88.02
19.88
2.87
3604
3470
3131
3117
3100
3073
3061
3059
3055
3004
3001
2963
2933
2929
76.45
16.62
2.37
υOH
3408 sbr
3402 w
3136 w
υNH
3124 w
υCH I
υCH I
υCH II
υCH II
υCH I
υCH II
υCH II
υasMe
υasMe
2.73
3.61
3.23
2.63
2.53
2.63
18.54
12.32
20.78
17.70
49.95
65.66
6.55
13.19
10.98
17.01
14.77
27.65
41.70
7.92
14.66
12.39
19.51
16.09
31.73
46.63
8.87
3079 w
3055 m
3039 w
3050 w
3040 w
3042 w
2999 w
2971 m
2976 w
υasCH2
33.02
43.58
34.35
29.48
35.53
30.42
2933 s
υsMe
2920 w
2883 w
2661 w
υsCH2
2887 br
2832 w
2759 w
2704 w
2558 w
2102 w
2029 w
1883 w
1810 w
1647 s
Overtones/combinations
1752
1661
1626
1607
1596
1576
1518
1513
1495
1477
1465
1461
1457
1410
1402
1394
1336
1311
1304
1277
1254
1249
1235
1205
1180
1178
1168
1122
1113
297.17
394.26
44.34
125.64
69.44
9.96
1730
1630
1616
1603
1589
1572
1508
1502
1478
1473
1463
1454
1411
1401
1376
1366
1363
1333
1315
1303
1291
1275
1237
1235
1225
1194
1168
1154
1111
173.50
92.65
31.75
63.43
140.84
5.30
1712
1609
1604
1589
1560
1559
1501
1497
1479
1472
1468
1459
1405
1397
1381
1346
1339
1319
1316
1297
1290
1268
1237
1233
1218
1188
1170
1153
1109
170.70
43.98
26.86
54.87
13.78
184.82
10.89
79.83
12.19
322.37
7.78
1630 s
1587 s
υC O
υPh I
1598 s
υPh II
υPh I
υPh II
υasNO2
υPh II
υPh I
1530 vs
1497 vs
1550 w
1508 m
1494 sh
1533 w
1504 s
167.28
49.95
286.85
3.81
92.82
58.43
312.36
10.79
9.54
δasMe
δNH
6.79
1468 w
1431 m
δasMe
υPh I, δCH2
υPh II, δOH
δOH
0.23
2.13
1.41
1457 w
1410 m
1452 m
1430 w
407.85
273.34
51.42
1.06
116.50
25.56
2.28
79.35
90.69
1.84
1383 m
1345 vs
1377 w
1378 w
1340 w
δsMe
328.42
259.58
0.58
12.33
433.60
8.58
υCN
9.69
υsNO2
ωCH2
υPh II
υCN
26.10
334.21
9.46
6.13
0.16
225.71
7.86
120.52
262.08
216.74
0.63
1304 vvs
90.64
179.69
7.65
1292 s
υPh I
270.91
1.39
1272 s
1272 s
υ(C-O)h
τCH2
1240 w
1244 w
3.68
2.52
28.90
140.90
7.73
υPh I
5.36
130.25
2.79
1220 s
1217 w
1180 w
δNH
2.46
1185 w
1184 w
1149 s
δCH II
ρMe
27.06
16.69
6.20
35.84
29.37
14.01
43.77
22.45
14.81
ρNH
1127 m
δCH II
c
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Copyright ꢀ 2009 John Wiley & Sons, Ltd.
J. Raman Spectrosc. 2010, 41, 381–390

Vibrational spectroscopy of 4-ethyl-N-(2ꢁ-hydroxy-5ꢁ-nitrophenyl)benzamide
Table 1. (Continued)
HF/6-31G∗
υ (cm−1
IR intensity
B3PW91/6-31G∗
υ (cm−1
IR intensity
B3LYP/6-31G∗
υ (cm−1
IR intensity
)
)
)
υ(IR) (cm−1
)
υ(Raman) (cm−1
)
υ(Raman) (cm−1
)
Assignments
1091
1074
1069
1057
1032
998
995
981
976
960
933
929
886
862
850
828
824
779
769
767
763
757
709
698
639
625
617
580
553
535
510
470
463
418
409
375
355
344
339
329
302
296
269
234
214
192
173
125
121
81
73.06
2.43
1107
1086
1067
1051
1037
998
952
950
935
928
920
903
871
836
823
806
795
780
767
764
747
732
695
682
639
624
620
577
553
534
506
475
464
451
407
399
360
353
350
332
320
296
268
235
215
190
174
136
122
89
5.6971
52.97
108.57
22.62
5.51
1109
1079
1063
1049
1038
999
952
941
931
925
920
902
869
837
823
800
794
776
769
761
746
724
693
680
636
628
621
577
553
534
508
475
464
450
408
402
362
352
347
332
320
297
270
236
212
191
175
138
123
90
13.91
56.61
103.51
20.75
6.88
1106 m
δCH II
1072 m
1066 sh
1072 w
δCH I
104.88
8.97
1069 m
δCH I
ρMe
6.35
δCH I
2.41
9.79
11.75
1.15
1015 w
949 w
δCH II
4.31
3.44
960 w
939 w
975 w
γ CH II
υC21C27
γ CH II
γ CH II
γ CH I
0.27
1.85
2.29
0.19
22.48
11.48
2.41
12.09
21.36
2.90
9.83
25.40
2.08
914 w
906 w
10.65
21.63
17.31
12.34
6.45
9.13
897 m
902 m
846 w
809 w
γ CH I
26.23
15.16
10.29
23.61
6.22
19.13
14.67
10.74
7.39
ωNH
847 m
827 m
γ CH II
Ring breath II
δNO2
829 w
14.92
5.83
14.88
5.17
γ CH II
RING I
ρCH2
17.59
21.44
59.08
0.96
1.66
0.84
772 m
717 w
1.28
1.65
759 w
743 m
727 w
698 w
δPh II, γ NH
18.70
34.24
15.60
12.28
19.52
0.31
16.90
29.16
15.40
11.80
19.81
0.30
δC O
11.64
8.90
730 w
ωNO2
γ Ph II
11.78
39.16
0.58
γ Ph I
641 m
632 m
618 w
643 w
616 w
550 w
δPh(X) II
δPh(X) I, γ OH
δPh II
5.69
2.25
2.88
601 w
534 w
37.58
2.06
27.25
2.26
25.46
1.85
γ Ph(X) I
γ Ph II
545 w
524 w
505 w
1.53
1.73
1.14
ρNO2
6.70
8.57
8.27
γ Ph II (X)
NH
14.54
1.89
54.45
17.48
32.90
13.42
0.19
50.80
13.40
37.96
13.07
0.34
476 w
δPh (X) I
δCN(X) I
δPh (X)II
γ PhII
1.19
0.13
412 w
402 w
30.14
5.82
2.30
3.01
δCC(X) II
γ Ph(X) I
δCO(X) I
Ch2
35.58
42.23
2.13
50.30
19.10
14.72
15.22
3.47
10.99
49.39
18.18
19.92
3.54
346 w
67.78
40.66
9.93
τMe
γ CC(X) II
τMe
6.10
6.43
266 w
217 w
180 w
13.27
0.22
4.37
4.24
244 vs
γ CO(X) I
γ CO(X) I
γ CN(X) I
δCN(X) I
γ CN(X) I
γ CN(X) I
γ CC(X) II
0.09
0.10
1.37
0.93
1.02
6.22
2.54
2.36
4.23
3.52
3.51
0.85
2.19
2.08
2.31
5.71
5.87
101 m
υ, stretching; δ, in-plane bending; γ , out-of-plane bending; τ, torsion; s, strong; m, medium; w, weak; v; very; br, broad; Ph I and Ph II, tri- and
para-substituted phenyl rings; X, substituent sensitive; subscript: as, asymmetric, s, symmetric.
c
J. Raman Spectrosc. 2010, 41, 381–390
Copyright ꢀ 2009 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/jrs

C. Y. Panicker et al.
a characteristic band near 1465 cm−1 in the IR and Raman spectra.
This mode is unambiguously correlated with the strong band
at 1457 cm−1 in the Raman spectrum. The twisting and rocking
vibrations of the CH2 group appear in the regions[48] 1260 10
and 800 25 cm−1. These modes are also assigned (Table 1).
For the methyl group, the asymmetric stretching vibration
is observed in the region 2940–3010 cm−1, and the symmetric
stretching appear in the region[48] 2840–2970 cm−1. The com-
puted wavenumbers of the modes corresponding to the υasCH3
and υsCH3 group are 3004, 3001, and 2933 cm−1. The asymmetric
deformations[48] of the methyl group are expected in the regions
1465 20 and 1445 25 cm−1. The overlap between the two
regions is quite considerable, so for many molecules the defor-
mations often coincide. The symmetric deformation[48] of methyl
group appears in the region 1380 20 cm−1. The B3LYP calcu-
lations give bands at 1479, 1468 and 1381 cm−1 as asymmetric
and symmetric deformations of the methyl group, respectively.
Also, the theoretically calculated val−u1es for rocking modes of the
methyl group are 1049 and 1170 cm , which are expected in the
regions[48] 1080 80 and 1170 95 cm−1. The torsional modes of
The most characteristic band in the spectra of the nitro
compounds are due to NO2 stretching vibrations, which are
the two most useful group wavenumbers, not only because of
their spectral position but also for their strong intensity.[48] In
nitro compounds, the antisymmetric NO2 stretching modes[48]
are located in the region 1580 80 cm−1. The symmetric NO2
stretching vibrations[48] are expected in the region 1380
20 cm−1. In substituted nitrobenzenes, υsNO2 appears strongly
at 1345 30 cm−1; in 3-nitropyridine[56] at 1350 20 cm−1; and
in conjugated nitroalkenes[57] at 1345 15 cm−1. In the present
case, the bands observed at 1530 cm−1 in the IR spectrum and
1550 cm−1 in the Raman spectrum are assigned as asymmetric
NO2 stretching modes. The symmetric NO2 stretching mode is
observed at 1345 cm−1 as a very strong band. The DFT calculations
give 1559 and 1339 cm−1 as asymmetric and symmetric stretching
NO2 vibrations. According to some investigators,[58–60] the NO2
scissoring[48] occur in the region 850 60 cm−1 when conjugated
to C C or aromatic molecules, with a contribution of the υCN,
which is expected to be near 1120 cm−1. For nitrobenzene,
δNO2 is reported[48] at 852 cm−1; for H2C CHNO2 at 890 cm−1
;
methyl group are observed below 400 cm−1
.
and for 1,3-dinitrobenzene at 904 and 834 cm−1. For the title
compound, the DFT calculations give the band at 800 cm−1 as the
deformation band of NO2. The band observed at 809 cm−1 in the
Raman spectrum is assigned as δNO2. In aromatic compounds, the
wagging mode ωNO2 is assigned at 740 50 cm−1 with moderate
to strong intensity, a region in which γ CH is also active.[48] ωNO2
is reported at 701 and 728 cm−1 for 1,2-dinitrobenzene and at 710
and 772 cm−1 for 1,4-dinitrobenzene[48]. For the title compound,
the band at 727 cm−1 in the IR spectrum, 717 cm−1 in the Raman
spectrum, and 724 cm−1 by DFT are assigned as the wagging
modes of NO2. In aromatic compounds, the rocking mode ρNO2
is active in the region 545 45 cm−1. Nitrobenzene[48] shows
this rocking mode at 531 cm−1. In the present case, the DFT
calculations give ρNO2 at 534 cm−1. Sundaraganesan et al.[61]
reported the NO2 deformation bands at 839, 744, and 398 cm−1
(experimental) and 812, 716, 703, and 327 cm−1 theoretically.
The identification of C–N stretching vibration is a difficult task
because mixing of several bands is possible in this region.
Silverstein et al.[53] assigned the C–N stretching absorption in
the region 1382–1286 cm−1 for aromatic amines. The C–N
stretching mode is reported at 1368 cm−1 for benzamide,[62] at
1382, 1307 cm−1 for benzotriazole[61] and at 1335 and 1331 cm−1
for 2,4-dinitrophenylhydrazine.[61] Primary aromatic amines with
nitrogen directly on the ring absorbs strongly at 1330–1260 cm−1
due to stretching of the phenyl carbon–nitrogen bond.[50] The
reported values of the C–N stretching modes are 1340 cm−1
(Raman), 1325 (calculated),[63] 1318 cm−1[64] and at 1332 (IR), 1315
(Raman), 1315 cm−1 (HF).[65] For the title compound, the B3LYP
The carbonyl stretching C O vibrations[48,54] are expected in
the region 1715–1680 cm−1 and in the present study this mode
appears at 1647 cm−1 in the IR spectrum and at 1630 cm−1 in
the Raman spectrum as a strong band. The B3LYP calculations
give this mode at 1712 cm−1. El-Shahawy et al.[52] reported a
value 1640 cm−1 in the IR spectrum as υC O for paracetamol.
The deviation of the calculated wavenumber for this mode can
be attributed to the underestimation of the large degree of π-
electron delocalization due to conjugation in the molecule.[55]
The intensity of the carbonyl group can increase because of
conjugation or formation of hydrogen bonds. The increase in
conjugation, therefore, leads to the intensification of the Raman
lines as well as increased IR band intensities. The conjugation
and influence of intermolecular hydrogen bonding result in the
lowering of the stretching wavenumber. The bands associated
with the C O stretching mode are found to be strongly and
simultaneously active in both IR and Raman spectra.
The NH stretching vibration[48] appears as a strong and broad
band in the region 3390 60 cm−1. For the title compound, the
strong band at 3408 cm−1 in the IR spectrum and 3402 cm−1 in
the Raman spectrum is assigned as the υNH mode. The calculated
value for this mode is 3470 cm−1. The NH stretching wavenumber,
which is very strong in the IR spectrum, is red-shifted by 62 cm−1
from the computed wavenumber (B3LYP). This indicates the
weakening of the NH bond resulting in proton transfer to the
neighboring oxygen.[54] The CNH vibration, in which the N and
H atoms move in opposite direction of the carbon atoms in the
amide moiety, appears at 1472 cm−1 theoretically, and, the CNH
vibration, in which the N and H atoms move in the same direction
of the carbon atoms in the amide group, appears at 1220 (IR),
1217 (Raman), and 1218 cm−1 (DFT).[49,50,52] The calculated value
of the NH rocking[52] is 1153 cm−1. The out-of-plane wagging[48]
of NH is moderately active with a broad band in the region
790 70 cm−1, and the band at 869 cm−1 (DFT) is assigned as this
calculations give the stretching mode of CN at 1346 cm−1
.
Since the identification of all the normal modes of vibration of
large molecules is not trivial, we tried to simplify the problem by
considering each molecule as a substituted benzene. Such an idea
has already been successfully utilized by several workers for the
vibrational assignment of molecules containing multiple homo
and hetero aromatic rings.[65–70] In the following discussion, the
tri-substituted and para-substituted phenyl rings are designated
as ring I and II, respectively. The modes in the two phenyl rings will
differ in wavenumber, and the magnitude of splitting will depend
on the strength of interaction between different parts (internal
coordinates) of the two rings. For some modes, this splitting
is so small that they may be considered as quasi-degenerate,
mode. El-shahawy et al.[52] reported this band at 720 cm−1
TheC–Nstretchingvibration[48] coupledwithδNHismoderately
.
to strongly active in the region 1275
55 cm−1. El-Shahawy
et al.[52] observed a band at 1320 cm−1 as this υC–N mode.
In the present case, the band at 1304 cm−1 in the Raman
spectrum is assigned to this mode. The DFT calculations give
the corresponding band at 1297 cm−1
.
c
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Copyright ꢀ 2009 John Wiley & Sons, Ltd.
J. Raman Spectrosc. 2010, 41, 381–390

Vibrational spectroscopy of 4-ethyl-N-(2ꢁ-hydroxy-5ꢁ-nitrophenyl)benzamide
and for other modes a significant amount of splitting may be
observed.[66–68,71]
The IR bands in the 2887–1810 cm−1 region and their
large broadening support the intramolecular hydrogen bonding
between the C O and OH groups.[74]
The aromatic CH stretching vibrations[48] absorb weakly to
moderately between 3120 and 3000 cm−1. The B3LYP calculations
give bands in the range 3055–3131 cm−1 as υCH stretching
modes. Experimentally, we have observed bands at 3124 and
3042 cm−1 in the IR spectrum and at 3136, 3079, 3055, and
3039 cm−1 in the Raman spectrum as CH stretching modes of the
phenyl rings.
SERS spectrum
The relative intensities in the SERS spectrum are expected to
differ significantly from normal the Raman spectrum due to
specific selection rules.[75] Surface selection rules suggest that
for a molecule adsorbed flat on the silver surface, its out-of-plane
bending modes will be more enhanced when compared to its
in-plane bending modes, and vice versa when it is adsorbed
perpendicular to the surface.[75,76] It is further seen that the
vibrations involving atoms that are close to the silver surface will
be more enhanced. When the wavenumber difference between
the Raman bands in the normal and the SERS spectrum is not
more than 5 cm−1, the molecular plane will be perpendicular to
the surface.[77] In 2-methylpyridine, Bunding et al.[78] noticed a
significant shift and broadening of the CH3 modes in the SERS
spectrum. They explained this in terms of the interaction of the
methyl group and the metal surface. In the present study, the
symmetricmethylstretchingmodeispresentintheSERSspectrum
at 2933 cm−1 and is absent in the normal Raman spectrum. It
should be related to the closeness of the methyl group to the
silver surface. This is justifiable because the motion in groups
directly interacting with the metal surface will be prominent in the
SERS spectrum.[79] Further, the CH2 and CH3 bands at 1452, 1378,
and 1149 cm−1 are also observed in the SERS spectrum, thereby
supporting the above argument. In the case of SERS spectrum of
β-hydroxy-β-methylbutanoic acid, the bands at 1447, 880, 725,
and 692 cm−1 due to CH2 and CH3 modes suggest that these
moieties assist the molecule to bind to the silver surface.[80] In
the SERS spectrum of 2-amino-5-nitropyridine,[81] the symmetric
NO2 stretching mode corresponds to the most intense band,
which appears broad and significantly downshifted from 1344 to
1326 cm−1 suggesting binding to silver through the lone pairs of
the oxygen atom. Carrasco et al.[82] observed the NO2 stretch in
the SERS spectrum at ∼1500 cm−1 with medium intensity, which
demonstrated the importance of the nitro group in regard to
the interaction with the metal surface. Further, they observed
the enhancement of υPh modes, revealing that the molecule is
oriented perpendicular to the metal surface, whereas the changes
that occur in the nitro group indicate that the interaction occurs
through oxygen atoms of the nitro moiety. The interaction induces
aπ-electronicredistributionprimarilyaroundboththenitrogroup
and the aromatic portion in the vicinity of the substitution site.
Also, Gao and Weaver[83] observed broadly and a downshift of the
corresponding band of nitrobenzene adsorbed on gold via a nitro
group. For the title compound, the symmetric stretching mode of
NO2 which is absent in the normal Raman spectrum appears at
1340 cm−1 in the SERS spectrum. Interaction through NO2 group
was also supported by the presence of modes at 1533, 730, and
534 cm−1. For sodium salicylate,[74] the υ(C–O)h stretch of the
hydroxyl group is present in the SERS spectrum at 1252 cm−1 and
this is indicative of the nearness of the OH group to the metal
surface. In the present case, υ(C–O)h appears at 1272 cm−1 with
very strong intensity in the SERS spectrum.
The benzene ring possess six ring-stretching vibrations of which
the four with the highest wavenumbers occurring near 1600,
1580, 1490 and 1440 cm−1 are good group vibrations.[48] With
heavy substituents, the bands tend to shift to somewhat lower
wavenumbers, and the greater the number of substituents on
the ring, the broader the absorption regions.[48] In the case of
C
O substitution, the band near 1490 cm−1 can be very weak.[48]
The fifth ring-stretching vibration is active near 1315 65 cm−1
,
a region that overlaps strongly with that of the CH in-plane
deformation.[48] The sixth ring-stretching vibration, the ring-
breathing mode, appears as a weak band near 1000 cm−1 in
mono-, 1,3-di-, and 1,3,5-trisubstituted benzenes. In the otherwise
substituted benzenes, however, this vibration is substituent-
sensitive and difficult to distinguish from other modes. The
ring-breathing mode for the para-substituted benzenes with
entirely different substituents[49] has been reported to be strongly
IR active with typical bands in the interval 780–840 cm−1. For the
title compound, this is confirmed by the band in the IR spectrum at
827 cm−1,whichfindssupportfromthecomputationalresults.The
ring-breathing mode of para-substituted benzenes are reported
at 804 and 792 cm−1 experimentally and at 782 and 795 cm−1
theoretically.[72,73] In asymmetric tri-substitued benzenes, when
all the three substituents are light, the wavenumber interval
of the breathing mode[49] is between 500 and 600 cm−1
.
When all the three substituents are heavy, the wavenumber
appears above 1100 cm−1. In the case of mixed substituents,
the wavenumber is expected[49] to appear between 600 and
750 cm−1. For the title compound, the phenyl ring I breathing
mode is observed at 776 cm−1 theoretically. For para-substituted
benzenes, the δCH modes are seen in the range 995–1315 cm−1
and for tri-substituted benzenes these modes are in the range[48]
1290–1050 cm−1. Bands observed at 1185, 1127, 1072, 1066, and
1015 cm−1 in the IR spectrum and at 1180, 1106, and 1069 cm−1
in the Raman spectrum are assigned as δCH modes. The DFT
calculation give these modes at 1188, 1109, 1079, 1063, 1038,
and 999 cm−1, as these modes and some of the bands are not
pure but contain significant contribution from other modes. The
CH out-of-plane deformations[48] are observed between 1000 and
700 cm−1. Generally, the CH out-of-plane deformations with the
highest wavenumbers are weaker than those absorbing at lower
wavenumbers. These γ CH modes are observed at 949, 897, and
847 cm−1 in the IR spectrum and at 960, 902, and 846 cm−1 in
the Raman spectrum. The strong CH out-of-plane deformation
band occurring at 840 50 cm−1 is typical for 1,4-di-substituted
benzenes.[48] For the title compound, a band is observed at
847 cm−1 in the IR spectrum. Again according to literature,[48,50]
a lower γ CH absorbs in the neighborhood 820 45 cm−1, but
is much weaker or infrared inactive. The DFT calculation gives a
γ CH at 794 cm−1 and no band is experimentally observed for this
mode. In the case of tri-substituted benzenes, two γ CH bands are
observed at 890 50 and 815 45 cm−1 in the IR spectrum. The
bands observed at 897 (IR), 902 (Raman), and 902 cm−1 (DFT) are
assigned to this modes.
Keeping in mind the behavior observed for molecules contain-
ing π-system adsorbed flat on the metal surfaces,[76,83–85] a purely
parallel orientation of the molecular skeleton with respect to the
surface appears unlikely in the light of the following arguments.
The ring-breathing mode in the SERS spectrum at 829 cm−1 ap-
pears as a very weak band. Also, the out-of-plane CH modes 975,
c
J. Raman Spectrosc. 2010, 41, 381–390
Copyright ꢀ 2009 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/jrs

C. Y. Panicker et al.
914, and 906 cm−1 and the in-plane CH mode at 1072 cm−1 also
Saeed et al.[90] reported C20 –O24
,
N33 –O34
,
N33 –O35,
suggest a tilted orientation of the molecule. The υPh modes are
N25 –C20, N25 –C11, and N33-C15 bond lengths are 1.2132,
1.2292, 1.2252, 1.3612, 1.4042, and 1.4632 ´Å for 2-nitro-N-(4-
nitrophenyl)benzamide. For the title compound, the bond lengths
obtained are 1.221, 1.2326, 1.2331, 1.3933, 1.4128, and 1.4614 ´Å,
respectively. For the benzamide moiety of the title compound, the
also present in the SERS spectrum at 1504, 1452, and 1430 cm−1
.
In the SERS spectrum of the title compound, the aromatic CH
stretching vibrations are observed as weak bands at 3050 and
3040 cm−1, which suggests that the phenyl ring II may be in a
position close to the perpendicular to the silver surface, possibly a
tilted position since the bands are weak.[77,86,87]
calculated values of the bond angles C20 –N25 –C11, C12 –C11 –N25
,
O24 –C20 –N25 O24 –C20 –C3, N25 –C20 –C3, C4 –C3 –C20 and
,
,
C2 –C3 –C20 are 122.7, 120.3, 122.1, 122.7, 115.2, 117.5, and
123.7◦, respectively. Sun et al.[89] reported the correspond-
ing angles as 124.7, 116.6, 123.1, 118.7, 118.3, 115.6, and
124.3◦, respectively. Also, the DFT calculations give the torsional
angles C15 –C13 –C11 –N25, N25 –C11 –C12 –C14, O24 –C20 –C3 –C2,
N25 –C20 –C3 –C2, O24 –C20 –C3 –C4, and N25 –C20 –C3 –C4 as
−178.3, −179.8, −158.2, 22.1, 20.8, and −158.9◦ around the ben-
zamide group, which are in agreement with the reported values[88]
178.5, −178.9, −16.8, 163.8, 161.6, and −17.8◦. The C20 –N25 bond
istwistedfromthephenylringIandII, asisevidentfromthetorsion
angles C12 –C11 –N25 –C20 = 60.5◦, C13 –C11 –N25 –C20 = −122.0◦,
and N25 –C20-C3 –C4 = −158.9◦, N25 –C20 –C3 –C2 = 22.1◦.
Analysis of organic molecules having conjugated π-electron
system×s and large hyperpolarizability using infrared and Raman
spectroscopies has evolved as a subject of research.[95] The
potential applications of the title compound in the field of
nonlinear optics demand the investigation of its structural
and bonding features contributing to the hyperpolarizability
enhancement, by analyzing the vibrational modes using the
IR and Raman spectra. The first hyperpolarizability (β0) of this
novel molecular system is calculated theoretically, based on the
finite-field approach. In the presence of an applied electric field,
the energy of a system is a function of the electric field. First
hyperpolarizability is a third-rank tensor that can be described by
a 3 3 × 3 matrix. The 27 components of the 3D matrix can be
reduced to 10 components because of Kleinman symmetry.[96]
The components of β are defined as the coefficients in the
Taylor-series expansion of the energy in the external electric field.
When the electric field is weak and homogeneous, this expansion
becomes
Geometrical parameters and hyperpolarizability
To the best of our knowledge, no X-ray crystallographic data of this
moleculehasyetbeenestablished.However,thetheoreticalresults
obtained are almost comparable with the reported structure
parameters of related molecules.[88–90] The carbon–oxygen
(phenolate) C12 –O31 distance of 1.3508 ´Å is in agreement with
the average distance of 1.362 ´Å found among phenols.[91] DFT
calculations give shortening of the angle C17 –C15 –N33 by 0.6◦ and
C13 –C15 –N33 by 1◦ from 120◦ at C15 position and C15 –N33 –O34
,
C15 –N33 –O35 by 2.2◦ from 120◦ at N33 position. This reduction in
angles reveals the hydrogen bonding between H19 and H16 atoms,
which is evident from the increase in the angles C17 –C15 –C13 by
1.5◦ and O34 –N33 –O35 by 4.4◦. The bond angles of the NO2 group
of the title compound O34 –N33 –O35 = 124.4, O34 –N33 –C15
=
117.8, and O35 –N33 –C15 = 117.8 are in agreement with the
values 123.5, 118.7, and 117.9 given by Saeed et al.[90]
At C3 position, the angle C4 –C3 –C20 is reduced by 2.5◦ and
C2 –C3 –C20 is increased by 3.7◦ from 120◦, and this asymmetry
of exocyclic angles reveals the interaction between O24 and
the phenyl ring II. The CC bond lengths in the phenyl ring lie
between 1.3888 and 1.4153 ´Å, whereas for the phenyl ring II, the
range is 1.3906–1.4032 ´Å. The CH bond lengths lie between
1.0826 and 1.0877 ´Å for phenyl ring I and between 1.0852
and 1.0876 ´Å for phenyl ring II. Here for the title compound,
benzene is a regular hexagon with bond lengths somewhere in
between the normal values for a singe (1.54 ´Å) and a double
(1.33 ´Å) bond.[92] According to Noveron et al.,[88] for complexes of
N-(4-pyridyl)benzamide, the bond lengths for C11 –N25, C20 –O24
,
C20 –N25, C20 –C3, C3 –C2, C3 –C4, and N25 –H26 are 1.3953, 1.2253,
1.3703, 1.4943, 1.3923, 1.3933, and 0.773 ´Å, respectively, and
the corresponding values for the title compound are 1.4128,
1.2210, 1.3933, 1.4977, 1.4019, 1.4016, and 1.0111 ´Å, respectively.
For N-(2-pyridyl)benzamide complexes,[89] the bond lengths for
C20 –O24, N25 –C20, N25 –C11, and C20-C3 are 1.2445, 1.3646, 1.4156,
and 1.4816 ´Å, respectively, while in the present case these bond
lengths are 1.221, 1.3933, 1.4128, and 1.4977 ´Å.
The C O and C–N bond lengths[23] in benzamide, acetamide,
andformamideare,respectively,1.2253,1.2203,1.2123and1.3801,
1.3804, 1.3683 ´Å.
According to the literature,[26,28,32,93] the changes in bond
length in C O and C–N are consistent with the following
interpretation: that is, hydrogen bond decreases the double
bond character of C O bond and increases the double bond
character of the C–N bond. The values of the angles C4 –C3 –C20
(117.5◦) and C3 –C20 –O24 (122.7◦) are smaller than those of
benzaldehyde,[94] 121.0 and 123.6. These differences are ascribed
to the steric repulsion between the H8 and H26 atoms. The dihedral
angle C2 –C3 –C20 –O24 was determined to be −158.2◦ by the
B3LYP method. On the contrary, the equilibrium structure of
benzaldehyde is planar.[94] The steric repulsion in the present case
is also considered to cause the nonplanar skeleton. The C3 –C20
bond length (1.4977 ´Å) is larger than the corresponding length of
benzaldehyde[94] (1.4794 ´Å) by 0.0183 ´Å.
ꢀ
ꢀ
ꢀ
1
2
1
6
E = E0 −
µiFi −
αijFiFj −
βijkFiFjFk
i
ij
ijk
ꢀ
1
−
γ ijklFiFjFkFl + . . .
24
ijkl
where E0 is the energy of the unperturbed molecule, Fi
is the field at the origin, µi, αij, βijk, and γ ijkl are the
components of dipole moment, polarizability, the first hyper
polarizabilities, and second hyperpolarizibilites, respectively. The
calculated first hyperpolarizability of the title compound is
4.559 × 10−30 esu, which is comparable with the reported values
of similar derivatives,[97] but the experimental value is not readily
available. We conclude that the title compound is an attractive
object for future studies of nonlinear optical properties.
In order to investigate the performance and vibrational
wavenumbers of the title compound, the root mean-square (RMS)
value and the correlation coefficient between calculated and
observed wavenumbers were calculated (Fig. 5). RMS values of
wavenumbers were evaluated using the following expression:[98]
ꢁ
ꢂ
ꢂ
ꢃ
n
ꢀ
1
2
RMS =
(υci alc − υei xp
)
n − 1
i
c
www.interscience.wiley.com/journal/jrs
Copyright ꢀ 2009 John Wiley & Sons, Ltd.
J. Raman Spectrosc. 2010, 41, 381–390

Vibrational spectroscopy of 4-ethyl-N-(2ꢁ-hydroxy-5ꢁ-nitrophenyl)benzamide
Figure 5. Correlation graph.
The RMS error of the observed Raman bands, IR bands, and the
scaled wavenumbers are found to be 38.54, 36.86 (HF); 23.28, 23.8
(B3PW91); and 18.23, 18.11 (B3LYP), respectively. Small differences
between experimental and calculated vibrational modes are
observed. Itmustbeduetothefactthathydrogen-bondvibrations
present in the crystal lead to strong perturbation of the infrared
wavenumbers and intensities of many other modes. Also, we state
that the experimental results are of the solid phase and theoretical
calculations are of the gaseous phase.
[7] S. Itaru, M. Seizo, K. Takashi, Chem. Abstr. 1973, 81(1974), 73387,
Japan Patent, 73, 37, 819.
[8] P. I. Braz Pedido, Chem. Abstr. 1981, 95(1981), 61812z, N80 04, 641.
[9] G. A. White, Pestic. Biochem. Physiol. 1989, 34, 255.
[10] I. Yalcin, B. K. Kaymakcioglu, I. Oren, E. Sener, O. Temiz, A. Akin,
N. Altanlar, Il Farmaco 1997, 52, 685.
[11] K. J. Pradhan, P. S. Variyar, J. R. Bandekar, Lebensm. Wiss. U-Technol.
1999, 32, 121.
[12] E. Aki-Sener, K. K. Bingol, I. Oren, O. Temiz-Arpaci, I. Yalcin,
I. N. Altanlar, Il Farmaco 2000, 55, 469.
[13] E. Aki-Sener, K. K. Bingol, O. Temiz-Arpaci, I. Yalcin, N. Altnlar, Il
Farmaco 2002, 57, 451.
[14] I. Yildiz-Oren, E. Aki-Sener, C. Ertas, O. Temiz-Arpaci, I. Yalcin,
N. Altanlar, Turk. J. Chem. 2004, 28, 441.
Conclusion
[15] I. Kobayashi, H. Muraoka, M. Hasegawa, T. Saika, M. Nishida,
M. Kawamura, R. Ando, J. Antimicrob. Chemother. 2002, 50, 129.
[16] T. Ertan, I. Yildiz, S. Ozkan, O. Temiz-Arpaci, F. Kaynak, I. Yalcin,
E. Aki-Sener, U. Abbasoglu, Bioorg. Med. Chem. 2007, 15, 2032.
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The FT-IR, FT-Raman, and SERS spectra of 4-ethyl-N-(2ꢁ-hydroxy-
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and the wavenumbers were calculated using different levels of
theory. The observed wavenumbers are found to be in agreement
with the calculated (B3LYP) values. The red shift of the NH
stretching wavenumber in the IR spectrum from the computed
wavenumber indicates the weakening of the NH bond resulting in
protontransfertotheneighboringoxygenatom.Thesimultaneous
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the charge transfer interaction through a π-conjugated path.
Optimized geometrical parameters of the title compound are in
agreement with the reported values. SERS studies reveal a tilted
orientation for the molecule and, the presence of methyl modes
in the SERS spectrum indicates the nearness of methyl group to
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Supporting information
Supporting information may be found in the online version of this
article.
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